The invention relates to a process for monitoring the coolant level in a cooling system, in particular in a motor vehicle.
A process for regulating a motor vehicle air-conditioning system is known from German Patent Document 37 06 152, in which sensor signals from a plurality of sensors are fed to a control and monitoring device of a coolant circuit of the cooling system. The sensor signals are linked together for the calculation, as a function of or with regard to all fed input values, of output signals guaranteeing an optimal operating method for the components located in the coolant circuit. As sensors in the coolant circuit, there are provided, in this case, a sensor for recording the hot-gas temperature on the output side of the compressor, a sensor for recording the injection temperature or the pressure of the coolant on the input side of the evaporator and a sensor for recording the suction pressure or the suction temperature on the input side of the compressor.
However, optimum functioning of a cooling system is only ensured, that is irrespective of the particular control process, if the coolant is filled to the correct level. This is particularly also the case with regard to environmental aspects.
For monitoring the coolant level in a cooling system, a process according to the earlier described type is known from Japanese Patent Document JP-Abstract M-1037, Oct. 19, 1990, Vol. 14/No. 481=JP-A-2-195164, according to which the hot-gas temperature and the pressure on the output side of the compressor, the condenser output temperature and the temperature and the pressure on the input side of the compressor are measured and from the measured pressure values there are derived temperature values thereto assigned. These decimal temperature values are related, in turn, to the log p-t graph of the coolant. Thus, an overheating of the coolant can be determined by calculation and can be analyzed as a function of the coolant level.
An object of the invention is to provide a substantially simpler process for coolant level monitoring, in order thereby to further optimize the operating method of known cooling systems.
This and other objects are achieved by the present invention which provides a process for monitoring the coolant level in a cooling system of a motor vehicle. The relative pressure and the temperature of the coolant are measured on the high-pressure side of the coolant circuit and the measured coolant temperature and a temperature derived from the pressure is appropriately evaluated with respect to the coolant level. The coolant temperature is derived from the measured pressure value on the basis of a coolant-specific function. An undercooling U of the coolant is determined by subtracting the measured coolant temperature from the derived coolant temperature, the undercooling U providing a measure of the coolant level.
In a conventional process related to an optimal system-filling and the limit line of the log p-t graph, the level is monitored by evaluating an overheating of the coolant, i.e. in the area of high temperatures and of specific enthalpy. By contrast, the present invention is based upon the recognition that an established undercooling of the coolant also constitutes a measure for its level, thereby offering the advantages that the coolant-specific function temperature=f (pressure) is easily obtained by mirroring the appropriate part-area of the limit line of the log p-t graph and that only a small measuring effort is necessary, since on the high-pressure side only two measured values have to be taken.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.